University team builds “NexusHaus” for U.S. Solar Decathlon

Solar power and rainwater: The NexusHaus uses almost only natural resources – and thereby protects the climate and groundwater. (Picture: UTA/TUM)

13.03.2015, Research news

A house that generates more electricity than its inhabitants consume – many examples of such “energy-plus houses” already exist. Students from the Technische Universität München (TUM) and the University of Texas at Austin (UTA) now go one step further: They are designing and building a plus-energy house that consists almost entirely of sustainable materials and is also equipped with an efficient water-treatment system. With their "NexusHaus", they are the only team with German participants to have qualified for the renowned U.S. Solar Decathlon Competition 2015. The initial construction work and tests on the house are now taking place in Austin.

Austin, like many cities in the southern U.S., is experiencing rapid population growth. Affordable living space is correspondingly scarce, particularly for singles, families and those with low incomes. Redensification, the construction of houses on sites that have already been built on, is one of the options available for increasing the supply of less expensive housing units. However, such “Accessory Dwelling Units” are reliant on existing infrastructure and put a further strain on the already precarious electricity and water supplies in many cities. Students from TUM and UTA are developing a house that is inexpensive to build and also fulfills key criteria of the so-called “cradle-to-cradle design”: It provides for the inhabitants’ electricity and water requirements more or less completely, and it is built almost entirely of renewable or reusable materials. The German-American team is in the running for the renowned U.S. Solar Decathlon award with its “NexusHaus”.

“Nexus”: linking the interior and exteriorThe NexusHaus is conceived as a one-story pavilion structure: Living and sleeping areas are separate and located next to each other in a modular arrangement. They are linked by the “Nexus” - an additional space that can be used as a sunroom, roofed patio, or extended living room as desired. By forming part of the ventilation system in summer and acting as a buffer between the cold exterior air and warm interior air in winter, the Nexus space ensures that the temperature in the house will always be pleasant.

In the students’ design concept, the term “nexus” does not refer exclusively to the area that connects the living and sleeping modules. It also refers to the linking of the energy and water supply in the residential environment: The NexusHaus harnesses enough electricity from the solar power modules on the flat roof to cover its inhabitants’ electricity requirements for lighting, household appliances and an electric car. Solar power is used as well for air conditioning. Combined with a heat pump the water circuit is cooled or heated. An integrated thermal storage system shifts cooling off-peak to low demand nighttime hours.

Processing rainwater to drinking water The NexusHaus will also cover most of its inhabitants’ water needs itself: To this end rainwater is collected in large storage tanks and processed to drinking water quality with the help of a filter system. The students are also exploring new tools for “urban farming” - the production of food in city environments. The water for the garden is gray-water from the washing machine, sink and shower. In addition, condenser water from the air conditioning system is processed in an aquaponics system and used to irrigate the food plants. The nutrients for the fruit and vegetables are provided by fish feces. The plants filter the water, in turn, and thus maintain a suitable habitat for the fish. This reduces the demand for water from the public water supply considerably, making residents less dependent on price variations. In addition, the groundwater reservoirs are preserved – an obvious plus in a climate region that has suffered the most severe droughts of recent decades over the last five years.

Building materials: healthy and sustainableThe team from Munich and Austin has also broken new ground in the selection of building materials for their house. Most of the components used are pollutant- and toxin-free, and mainly consist of renewable raw materials or materials that can be easily dismantled into their constituent parts to facilitate recycling. The facade is constructed almost completely of the renewable raw material wood, and cradle-to-cradle certified ceramic tiles are used in the bathroom. The NexusHaus inhabitants and visitors can also access information about the origin and recyclability of the materials used through QR codes mounted on the exterior of the building.

Competition finale with washday and film eveningThe young architects have been carrying out the initial construction work on the NexusHaus since early March. The living and sleeping modules will be completed and the energy and water systems tested by the summer. The house will then be transported to Irvine, California, where the finale of the Solar Decathlon competition will take place from October 8 to 18, 2015.

The aspects of the competition houses to be evaluated by a jury include the architecture, market appeal, and technology. The university teams are also required to compete in some rather unusual disciplines: Over the course of one week they must wash and dry eight loads of laundry and organize two dinner parties and a movie evening for the neighbors. “The inhabitants of an energy- and material-saving house also enjoy a very good quality of life,” says Professor Werner Lang from the Technische Universität München. The NexusHaus is fitted with modern building services technology that is controlled using a home management system designed by the students.

The cost-efficiency of the NexusHaus concept will also be another plus-point for the competition: “The NexusHaus shouldn’t just offer an optimum ecological balance, it should also make a positive contribution to the local community,” says Professor Petra Liedl, who is supporting the university team on the UT Austin side. “We can add or remove modules as required – and in this way offer people with different backgrounds a comfortable living environment.”

About the Solar DecathlonThe Solar Decathlon is a biennial competition organized by the U.S. Department of Energy(DoE). It challenges collegiate teams to design, build, and operate 1,000-square foot solar-powered houses that are affordable, energy-efficient, and innovative. The DoE selected 20 collegiate teams to compete in Solar Decathlon 2015. The competition will take place in October 2015 at Orange County Great Park in Irvine, California. During the course of the week each team earns points through 10 contests, either juried or measured, designed to gauge the houses’ energy performance, livability, and affordability.